Check cache_parent_physical_bone when rebuilding parent cache

(cherry picked from commit 96fe795bdb3b2b91b4b09dff1692633493ff2be1)

scene/3d/skeleton.cpp

@@ -666,7 +666,7 @@ void Skeleton::_rebuild_physical_bones_cache() {
 	const int b_size = bones.size();
 	for (int i = 0; i < b_size; ++i) {
 		PhysicalBone *parent_pb = _get_physical_bone_parent(i);
-		if (parent_pb != bones[i].physical_bone) {
+		if (parent_pb != bones[i].cache_parent_physical_bone) {
 			bones.write[i].cache_parent_physical_bone = parent_pb;
 			if (bones[i].physical_bone) {
 				bones[i].physical_bone->_on_bone_parent_changed();